Tumors that express mutant protein kinases are usually dependent upon them for growth and survival. Activating mutations in FGFR3 occur in over half of low-grade non-muscle invasive bladder cancers (BCs) and in a quarter of muscle-invasive tumors, and small molecule and antibody-based FGFR3 inhibitors have exhibited potent growth-inhibitory activities in some BC cell lines and xenografts in preclinical studies. However, clinical translation of these observations has not occurred, in part because dose escalation trials have revealed that FGFR inhibitors produce some toxicity, and whether the extent of target inhibition at non-toxic doses is sufficient to produce apoptosis and/or growth arrest is not clear. We have assembled a collaborative group involving the GU Cancers team at Astra-Zeneca and Dr. Margaret Knowles (University of Leeds, UK) to conclusively determine the value of FGFR3 as a therapeutic target in BC. Our approach will be to use our unique panel of cell lines and xenografts to (1) isolate biomarkers that predict FGFR3 dependency better than FGFR3 mutational status alone and (2) develop pharmacodynamic approaches to determine the extent of tumor FGFR3 pathway inhibition and correlate it with biological response. We will also explore the effects of the novel tumor suppressive forerunner gene ARL11 on Ras pathway activation and define the relationships between ARL11 downregulatlon, FGFR3 and Ras mutational status, and Ras pathway activation in primary tumors, studies that are based on novel findings obtained in Project 1. We will then perform a neoadjuvant clinical trial to determine whether the doses of AZD4547 that can be safely achieved in patients produce sufficient target inhibition to cause apoptosis and/or growth arrest in primary tumors. This methodical approach will provide the strong mechanistic information required for the intelligent design of subsequent Phase II studies in low-grade and muscle-invasive BCs as well as in hematological and other tumors.